This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. African Americans, as compared to European Americans, have a higher prevalence and incidence of hypertension and experience higher rates of hypertensive complications [unreadable]in particular, stroke and end-stage renal diseasel. Furthermore, several studies have suggested that blood pressure might be more sensitive to sodium depletion or salt loading in African Americans than in European Americans. However, researchers have not consistently observed this ethnic difference in normotensive and hypertensive participants or in women and men. In the Dietary Approaches to Stop Hypertension (DASH) [unreadable]Sodium Trial, African Americans showed a greater blood pressure response to dietary sodium restriction than non-African Americans, but only on the control diet, and not on the DASH diet. We randomly recruited nuclear families of black South African ancestry and nuclear families of white Belgian ancestry. We measured the fractional excretion of sodium (FENa) and estimated the fractional renal sodium reabsorption in the proximal (RNaprox) and distal (RNadist) tubules from the clearances of endogenous lithium and creatinine. In multivariable analyses, we studied the relation of RNaprox and RNadist with the fractional excretion of sodium (FENa) and estimated the heritability of RNaprox and RNadist. Segmental sodium reabsorption along the nephron is highly heritable, but the capacity for regulation in the proximal and postproximal tubules differs between whites and blacks. Of the filtered sodium load, black participants reabsorb more than white participants in the proximal nephron and less postproximally. In another study, studying both African family members and unrelated Caucasions, SNPs in and around the ABCB1 gene were investigated for association with glomerular filtration rate (GFR). The 2677T and 3435T alleles were associated with significantly higher GFR, pointing to a new candidate gene for nephropathy in humans.